\documentclass{minimal}
\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{pgfplots.groupplots}

\begin{document}
\pgfplotsset{
	% override style for non-boxed plots
	% which is the case for both sub-plots
	every non boxed x axis/.style={}
}
\begin{tikzpicture}
	\begin{groupplot}[
			group style={
					group name=my fancy plots,
					group size=1 by 2,
					xticklabels at=edge bottom,
					vertical sep=0pt
				},
			width=8.5cm,
			xmin=-6, xmax=6
		]

		\nextgroupplot[ymin=45,ymax=80,
			ytick={60,80},
			axis x line=top,
			axis y discontinuity=parallel,
			height=4.5cm]
		\addplot {x*0};
		\addplot {x^2+50};

		\nextgroupplot[ymin=0,ymax=5,
			ytick={0},
			axis x line=bottom,
			height=2.0cm]
		\addplot {x*0};
		\addplot {x^2+50};
	\end{groupplot}
\end{tikzpicture}

\end{document}
